Conventional vehicle lights have employed a high intensity discharge lamp (HID lamp with approximately 3200 lm) and a halogen bulb (with 1000 to 1500 lm) as a light source. In order to reduce the power consumption and miniaturize the entire body size of the light, a projector type vehicle light that employs a semiconductor light emitting device as a light source is proposed in, for example, Japanese Patent Application Laid-Open No. 2003-317513.
Consider the case where an LED is employed as a light source semiconductor light emitting device. Such an LED has a luminous intensity as low as approximately 400 lm. Accordingly, a plurality of lamp units each including an LED are typically combined to ensure a desired light intensity and to improve the light distribution performance. When the vehicle light is of a projector type, the light emitted from the semiconductor light emitting device is collected and reflected by an elliptic reflector towards a projection lens to form a light distribution pattern suitable for, for example, a vehicle headlight. When a plurality of LED lamp units are combined within a limited space for installing such a headlight, a projection lens having a corresponding size cannot be installed within such a limited space due to the size, posing a problem in which the light utilization efficiency deteriorates to lower the light intensity.
In order to increase the light intensity at the center of the light distribution pattern, it would be conceivable to incline the light source so that the light illumination direction of the light source is adjusted with respect to the position of the reflector that is disposed on or near the center axis of a projection lens. In this case, it would be difficult and sometimes impossible to obtain sufficient light intensity. Accordingly, the application of a large current to a semiconductor light emitting device can be conceivable in order to increase the light intensity sufficient for a vehicle headlight. In this case, however, heat generation can be significant, and in some cases the semiconductor light emitting device can emit only a smaller amount of light than that in a normal condition or cannot be lit depending on the performance of the device due to the heat generation. In addition, the high current high heat environment may shorten the service life of the semiconductor light emitting device. To take a countermeasure against these problems, effective cooling of the semiconductor light emitting device to be supplied with a large current has been examined. One example of such a countermeasure is to provide a heat dissipation member (for example, a heat sink) to a semiconductor light emitting device (see, for example, Japanese Patent Application Laid-Open No. 2006-269271).